Quantum noise scaling in continuously operating multiparameter sensors

TL;DR

This study experimentally investigates quantum noise sources in multiparameter quantum sensors, revealing fundamental scaling laws and trade-offs that define their quantum limits of operation.

Contribution

It provides the first comprehensive experimental mapping of quantum noise mechanisms and their scaling in continuously operating multiparameter quantum sensors.

Findings

Photon shot noise, spin projection noise, and back-action noise scale differently with probe power.

Back-action noise exhibits quadratic dependence on pump photon flux.

Quantum noise limits are established for optimal sensor operation.

Abstract

We experimentally investigate the quantum noise mechanisms that limit continuously operating multiparameter quantum sensors. Using a hybrid rf-dc optically pumped magnetometer, we map the photon shot noise, spin projection noise, and measurement back-action noise over an order of magnitude in probe power and a factor of three in pump power while remaining quantum-noise-limited. We observe linear, quadratic, and cubic scaling of the respective total noise powers with probe photon flux, together with a quadratic dependence of back-action on pump photon flux, in quantitative agreement with a stochastic Bloch-equation model. At higher probe powers, additional probe-induced relaxation modifies the spin-noise spectrum while preserving the integrated noise scaling. Our results reveal fundamental, resource-dependent trade-offs unique to continuously monitored multiparameter sensors and establish experimentally the quantum limits governing their optimal operation.